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'[PIC] ID on a transmitter and receiver'
2004\08\25@212924 by n Zulhelmi Wan Ahmad Kamar

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Hi,
I'm creating an ultrasonic tracking device in which i have 4
transmitter and 1 receiver.  For that i will need to create an ID for
the receiver to distinguish where it is coming from.  Basically, from
there, i will calculate the time difference betwen the transmitter to
locate the position.

Anyway, my question, how can i distinguish the id for the receiver
part?  I was thinking of putting a constant delay for each transmitter
to transmit but how can I make sure my PIC18f252 produce an exact
delay of a certain millisecond or something.  It would need to be
exact isn't it?  Therefore, looping to create delay is out of the
question.

Another thing, on the transmitter part, how do i send the id?  I was
thinking about sending bit by bit but that would take up lots of
coding..  Any suggestions?

Do you guys think I need to implement Hamming Code for the code
correction or is that only applicable to RF design?

Thank you in advance.

From - Wan.

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2004\08\25@214004 by Engineering Info

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Why not modulate the ultrasonic frequency with an audio tone.  4
seperate tones for the 4 seperate transmitters.

Wan Zulhelmi Wan Ahmad Kamar wrote:

{Quote hidden}

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2004\08\25@214627 by SavanaPics

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There is a transmitter IDing device that the Hams use. I am not sure of where
to get it, but if you are intersted, contact me offline and I will see if I
can get you some information on it


Eddie Turner, kc4awz

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2004\08\25@215251 by n Zulhelmi Wan Ahmad Kamar

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Sorry, forgot to mention that i can't use an external device that
already have the built in function.  I have to use the PIC18f to do
its functionality.  It's practically reinventing the wheel, i know.

Thanks.
From  - Wan

On Wed, 25 Aug 2004 21:46:00 EDT, spam_OUTsavanapicsTakeThisOuTspamaol.com <.....savanapicsKILLspamspam@spam@aol.com> wrote:
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2004\08\25@215911 by Shawn Wilton

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Why do you *have to* use the 18f?  Is this a school project?


Shawn Wilton
Junior in CpE
MicroBiologist

Phone: (503) 881-2707
Email: shawnspamKILLspamblack9.net

http://black9.net


Wan Zulhelmi Wan Ahmad Kamar wrote:
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2004\08\25@220554 by n Zulhelmi Wan Ahmad Kamar

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Yes.. It's part of my final year project.  I've got the receiver and
transmitter part almost done.  It's just that the PIC18f is going
nowhere at the moment.

On Wed, 25 Aug 2004 18:58:19 -0700, Shawn Wilton <shawnspamspam_OUTblack9.net> wrote:
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2004\08\25@225148 by Engineering Info

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Why is that every post I make seems to be ignored.  I throw out a
suggestion and it seems like nobody even gives me the time of day that I
even exist.  IT IS REALLY EASY.  MODULATE THE TRANSMITTER.  Ok, so you
can't use any external componants to make an audio signal but you can
still use a large number of encoding methods that you can PWM the
ultrasonic device with. PWM at various frequencies an capture the timing
at the receiver or send out a series of short and long pulses and
capture it like RS-232. You can even pulse it like Morse code for all I
care.

Wan Zulhelmi Wan Ahmad Kamar wrote:

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2004\08\26@020357 by n Zulhelmi Wan Ahmad Kamar

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Hello.. Sorry about that.. The problem is if I modulate the
transmitter, wouldn't i need a receiver for each transmitter?  In my
circuit, I have 4 transmitter going to 1 receiver in which i will need
to calculate the time difference between arrival of the transmitter.



On Wed, 25 Aug 2004 19:51:08 -0700, Engineering Info
<EraseMEengineering-infospamearthlink.net> wrote:
{Quote hidden}

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2004\08\26@032610 by Russell McMahon

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> Why is that every post I make seems to be ignored.

They ignore a large portion of mine - why shouldn't they ignore you :-)
(Hint: If you post often enough some HAVE to get answered).

> I throw out a
> suggestion and it seems like nobody even gives me the time of day

It's 6:44pm on Thursday August 26th here at the leading edge of the world.
(See, from me you get not only time of day, but date as well. :-)  )

> IT IS REALLY EASY.  MODULATE THE TRANSMITTER.  ...

ID is, I think, the easy part. I think ranging (which this is about) is
going to be a little difficult. You have to get the trip time or the round
trip time.
Probably you need to do something like send a pulse from the master,
receiveit at a slave and then repeat it a controlled time after that. master
measures time form sending a pulse to getting one back. This could easily
handle the IDs as well.
eg
Master sends a pulse at t0
Slaves receive pulse at trn where n is 1 to 4 for slaves 1 to 4.
Slave 1 replies at td1 after seeing the pulse and master sees this td1 later
Slave 2 replies at td2 after seeing the pulse and master sees this td2 later
and so on.

Total trip time from the asters point of view is

Slave 1    2 x tr1+ td1
Slave 2    2 x tr2+ td1
Slave 3    2 x tr3+ td1
Slave 4    2 x tr4+ td1

As td1, td2, td3, td4 are known then trn can be easily calculated.

Say the maximum distance is 10 metres.
Speed of sound in air is about 333 metres/second.
2 x 10m = 20m = max real round trip distance.
tmax = 20/333 = 60 mS

If you set eg
td1 = 70 mS
td1 = 75 mS
td1 = 80 mS
td1 = 85 mS

Then replies will start to arrive in ......................

Aaaaaargh! :-)
Not quite that easy, is it?
If eg slave 2 is close and slave 1 is at max distance then replies can start
to overlap depending on the reply delays.
This can easily be sorted out with a but more effort.

Master sends distinctive "sync" signal. eg several pulses o whatever.
THEN sends a pulse which S1 responds to with fixed but minimal delay.
THEN another pulse which S2 responds to etc.
Round robin polling.

OR ... add your polling scheme here.

The (always arguable) advantage over eg Engineering Info's solution of
modulatin the signal is that you are only ever dealing with pulsed full
level signals which MAY be easier to generate and detect and MAY have more
range. Maybe not. One disadvantage is the possibiloity of confusion if the
sync signal gets misinterpreted - but this should come right next time
round.

That should be one way to progress your project :-)
Suggestion: When asking for help regarding an assignment it is a good idea
to say immediately that that is what you are doing. People will be  alittle
less hand holding BUT will be more likely to be happy to provide an
appropriate level of ongoing assistance.



Thoughts?


       Russell McMahon

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2004\08\26@032815 by Engineering Info

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4 cars are driving towards each other and all come to the same four way
intersection.  All 4 cars cannot go through the intersection at the same
time.  What do you do?  You take turns.

Wan Zulhelmi Wan Ahmad Kamar wrote:

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2004\08\26@053233 by Stef Mientki

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Wan Zulhelmi Wan Ahmad Kamar wrote:

>Hi,
>I'm creating an ultrasonic tracking device in which i have 4
>transmitter and 1 receiver.
>
Why not use 1 transmitter and 4 receivers ;-)
Stef Mientki

>
>

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2004\08\27@001957 by Engineering Info

picon face
Russell McMahon wrote:

>>Why is that every post I make seems to be ignored.
>>
>>
>
>They ignore a large portion of mine - why shouldn't they ignore you :-)
>(Hint: If you post often enough some HAVE to get answered).
>
I accept the fact that I will post a question and only sometimes will it
get answered.  I accept the fact that I may ask a question that nobody
actually has the answer for.  I accept the fact that someone may look at
my Subject line and hit delete without reading it.  What I think is bad
is when someone asks a question looking for help and completely ignores
you when you try and help them with an answer.

>>I throw out a
>>suggestion and it seems like nobody even gives me the time of day
>>
>>
>
>It's 6:44pm on Thursday August 26th here at the leading edge of the world.
>(See, from me you get not only time of day, but date as well. :-)  )
>
I just love dealing with people world wide with 24 seperate time zones.
You send me the message at 6:44pm on the 26th and I received the message
at 12:05AM on the 26th.

>>IT IS REALLY EASY.  MODULATE THE TRANSMITTER.  ...
>>
>>
>
>ID is, I think, the easy part. I think ranging (which this is about) is
>going to be a little difficult. You have to get the trip time or the round
>trip time.
>
Yes, ID is probally the easiest part of his project.  Wan also didn't
mention what method he was going to use to sync the transmitter to the
receiver.  All the message says is 4 transmitters and 1 receiver.  Could
be that he has one board with 4 transmitters pointing in seperate
directions (north, south, east, west) and one omni-direction receiver in
the center of the board.  This would be easy to sync.  Or does he have 4
transmitters scattered around the room (I.E. one in each corner) and a
portable receiver.  That would be much harder to work with.

>Suggestion: When asking for help regarding an assignment it is a good idea
>to say immediately that that is what you are doing. People will be  alittle
>less hand holding BUT will be more likely to be happy to provide an
>appropriate level of ongoing assistance.
>
Also thanking someone for an answer (even if it is wrong) would let them
know that you listened.  I don't mind being told my answer is wrong, I'm
used to it.  My wife says I wrong all the time.  But not letting someone
know your listening makes them not even what to try and help in the
first place.

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2004\08\27@002329 by Shawn Wilton

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He who has no name,
Thank you.

> Also thanking someone for an answer (even if it is wrong) would let them
> know that you listened.  I don't mind being told my answer is wrong, I'm
> used to it.  My wife says I wrong all the time.  But not letting someone
> know your listening makes them not even what to try and help in the
> first place.
>
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